riscv: define mtvec CSR with macro helpers

Uses the CSR macro helpers to define the `mtvec` CSR register.

Authored-by: rmsyn <github@weathered-steel.dev>
Reviewed-by: romancardenas <rcardenas.rod@gmail.com>

riscv/src/register/mtvec.rs

@@ -1,50 +1,65 @@
 //! mtvec register
 
-/// mtvec register
-#[derive(Clone, Copy, Debug)]
-pub struct Mtvec {
-    bits: usize,
+use crate::result::{Error, Result};
+
+const MASK: usize = usize::MAX;
+const TRAP_MASK: usize = 0b11;
+
+read_write_csr! {
+    /// mtvec register
+    Mtvec: 0x305,
+    mask: MASK,
+}
+
+csr_field_enum! {
+    /// Trap mode
+    TrapMode {
+        default: Direct,
+        Direct = 0,
+        Vectored = 1,
+    }
 }
 
-/// Trap mode
-#[derive(Copy, Clone, Debug, Eq, PartialEq)]
-pub enum TrapMode {
-    Direct = 0,
-    Vectored = 1,
+read_write_csr_field! {
+    Mtvec,
+    /// Accesses the trap-vector mode.
+    trap_mode,
+    TrapMode: [0:1],
 }
 
 impl Mtvec {
-    /// Returns the contents of the register as raw bits
+    /// Returns the trap-vector base-address
     #[inline]
-    pub fn bits(&self) -> usize {
-        self.bits
+    pub const fn address(&self) -> usize {
+        self.bits & !TRAP_MASK
     }
 
-    /// Returns the trap-vector base-address
+    /// Sets the trap-vector base-address.
+    ///
+    /// # Note
+    ///
+    /// Panics if the address is not aligned to 4-bytes.
     #[inline]
-    pub fn address(&self) -> usize {
-        self.bits - (self.bits & 0b11)
+    pub fn set_address(&mut self, address: usize) {
+        self.try_set_address(address).unwrap();
     }
 
-    /// Returns the trap-vector mode
+    /// Attempts to set the trap-vector base-address.
+    ///
+    /// # Note
+    ///
+    /// Returns an error if the address is not aligned to 4-bytes.
     #[inline]
-    pub fn trap_mode(&self) -> Option<TrapMode> {
-        let mode = self.bits & 0b11;
-        match mode {
-            0 => Some(TrapMode::Direct),
-            1 => Some(TrapMode::Vectored),
-            _ => None,
+    pub fn try_set_address(&mut self, address: usize) -> Result<()> {
+        // check for four-byte alignment
+        if (address & TRAP_MASK) != 0 {
+            Err(Error::InvalidFieldVariant {
+                field: "mtvec::address",
+                value: address,
+            })
+        } else {
+            self.bits = address | (self.bits & TRAP_MASK);
+            Ok(())
         }
     }
 }
-
-read_csr_as!(Mtvec, 0x305);
-
-write_csr!(0x305);
-
-/// Writes the CSR
-#[inline]
-pub unsafe fn write(addr: usize, mode: TrapMode) {
-    let bits = addr + mode as usize;
-    _write(bits);
-}